Display panel or portion thereof with a graphical user interface



FIG. 1 is a front view of a display panel or portion thereof with a graphical user interface showing our new design; and,

FIG. 2 is another front view thereof shown in a different broken line environment.

The outermost broken line rectangle illustrates a display panel or portion thereof and forms no part of the claimed design. The remaining broken lines illustrate portions of a graphical user interface or a mixed reality environment and form no part of the claimed design. 

CLAIM The ornamental design for a display panel or portion thereof with a graphical user interface, as shown and described. 